This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 0000481-2 filed in Sweden on Feb. 15, 2000; the entire content of which is hereby incorporated by reference.
1. Technical Field of the Invention
The present invention pertains to the field of methods and devices relating to battery temperature regulation, and more particularly to the part of this field concerned with temperature regulation of batteries having a preferred operating temperature range.
2. Background and Related Art
Many devices include one or more batteries for use in the operation of the devices. For example, it is common for portable devices to include one or more batteries as a supply of power. Furthermore, it is not uncommon for fixed devices to include one or more batteries as a backup in case of a power failure of an external power supply.
A lifetime of a battery often depends strongly on the temperature of the battery. In most batteries there is an electrolytic process in a liquid solution. If the temperature of the battery is above a preferred operating temperature range associated with the battery, the liquid will quickly dry out and electrodes of the battery will be damaged or worn out. Peaks in the temperature of the battery, even of relatively short durations, can therefore shorten the operating lifetime of the battery immensely. If, instead, the battery temperature is below the preferred operating temperature range, a performance of a galvanic process in the battery is degraded, thereby causing a decrease in voltage and charge of the battery. Consequently, the battery will have to be recharged more often, resulting in a reduction of a lifetime of the electrodes of the battery.
For example, if a lead battery is subjected to peak temperatures over 35xc2x0 C., the lifetime of the battery will be reduced with as much as 30-50%. Similarly, the useful lifetime of the lead battery will to some extent be reduced, should the battery be subjected to temperatures below 0xc2x0 C.
If, due to temperature extremes, the lifetime of the battery is reduced, this will result in increased costs, including costs for a replacement battery as well as working costs for changing the batteries. It is, therefore, desirable to maintain the temperature of the battery within the preferred operating temperature range at all times, in order to obtain an increased lifetime of the battery.
Today it is common to regulate the temperature of batteries using Air Conditioning Units (ACU). However, a drawback is that the ACUs are fairly complicated and expensive.
In U.S. Pat. No. 5,343,368 is disclosed a portable device having a passive mechanism for regulating the temperature of a battery associated with the portable device. The battery is surrounded by a blanket, which is in thermal communication with the battery and which contains a phase change material (PCM)xe2x80x94i.e. a material that changes from one state to another maintaining an essentially constant phase change temperature. The phase change material has a phase change temperature corresponding to an optimal operating temperature of the battery. When the portable device is received in an associated recharging stand, the phase change material will either be cooled or heated, depending on ambient temperature conditions. If an ambient temperature is above the optimal operating temperature, the phase change material will be refrigerated to a temperature below the phase change temperature (solid state). If, instead, the ambient temperature is below the optimal operating temperature, the phase change material will be heated to a temperature above the phase change temperature (liquid state). Consequently, the phase change material will serve to maintain the temperature of the battery at essentially the optimal operating temperature until all of the phase change material has changed phase from solid to liquid or from liquid to solid, whichever applies. However, once all of the phase change material has undergone a change of phase, the temperature of the battery will no longer be maintained at the optimal operating temperature. Furthermore, if there is a sudden change in the ambient temperature, for example from very hot to very cold, the phase change material will completely fail to maintain the battery at its optimal operating temperature.
The present invention addresses mainly the problem of obtaining methods and devices for temperature regulation of one or more batteries having preferred operating temperature ranges.
The problem is solved in short according to the following. Phase change material having a phase change temperature within the preferred operating temperature range is employed in order to maintain the battery temperature within the preferred operating temperature range during extreme ambient temperature conditions. When the ambient temperature so allows, a transfer of heat between the phase change material and ambient medium is effected for quickly restoring the capability of the phase change material to maintain the battery temperature at the phase change temperature.
A main object of the present invention is to regulate the temperature of one or more batteries, and the invention includes methods as well as devices for accomplishing this object.
The above-stated problem is solved in more detail according to the following.
For preventing the battery temperature from exceeding the preferred operating temperature range, it is preferred that the phase change temperature is in an upper portion of the preferred operating temperature range. The phase change material is thermally insulated from the ambient medium when the ambient temperature is above the phase change temperature. When, instead, the ambient temperature is in a selected range below the phase change temperature, a transfer of heat from the phase change material to the ambient medium is provided.
For preventing the battery temperature from falling below the preferred operating temperature range, a phase change material is used having, preferably, a phase change temperature in a lower portion of the preferred operating temperature range. The phase change material is thermally insulated from the ambient medium when the ambient temperature is below the phase change temperature. When, instead, the ambient temperature is in a selected range above the phase change temperature, a transfer of heat from the ambient medium to the phase change material is provided.
The invention has several advantages. The invention provides temperature regulation that greatly extends the lifetime of batteries, thereby considerably reducing costs. The temperature regulation provided according to the invention is also fairly simple and cheap. Furthermore, the invention uses the ambient medium in a very efficient way. When the ambient temperature so allows, the ambient medium is used to quickly return the phase change material to a temperature state which allows the phase change material to be used for maintaining the battery temperature essentially at the phase change temperature.
The invention will now be described further using preferred embodiments and referring to the drawings.